1. Field of the Invention
The present invention relates to a spectrophotometer and spectrophotometry capable of measuring intensity of light transmitted through a target sample and, more particularly, to a spectrophotometer provided with a precision drive means at its light intensity measuring unit for precisely moving said light intensity measuring unit, thus precisely measuring light intensity at any desired points, the present invention also relating to a spectrophotometry using such a spectrophotometer.
2. Description of the Prior Art
A conventional spectrophotometer and a spectrophotometry using such a conventional spectrophotometer will be described as follows:
FIG. 1 shows the construction of a conventional spectrophotometer. As shown in the drawing, the conventional spectrophotometer 100 comprises a light source 10 emitting a light beam having a predetermined wavelength range, and an optical fiber 20 guiding the light beam from the light source 10 to a target sample 30. The spectrophotometer 100 also comprises a spectrometer head 40 and a signal-processing unit 90. The spectrometer head 40 receives the light beam transmitted through the target sample 30, and diffracts the light beam into discrete wavelengths to produce optical spectra, and measures light intensities of the optical spectra. The signal-processing unit 90 receives spectrometric analysis data of the target sample 30 from the spectrometer head 40, and reproduces the distribution of light intensities of the spectra.
In the above spectrophotometer 100, the spectrometer head 40 comprises a reflective diffraction grating 50, a concave mirror 60, and a photodiode array 70. The reflective diffraction grating 50 is used for diffracting the light beam, transmitted through the target sample 30, into discrete wavelengths to produce optical spectra. The concave mirror 60 reflects the diffracted light from the diffraction grating 50, while the photodiode array 70 measures the intensity of incident light reflected by the concave mirror 60.
The photodiode array 70 comprises a plurality of photodiodes 80 linearly arranged on a longitudinal mount at regular physical intervals xe2x80x9cCxe2x80x9d. The photodiodes 80 are devices, each of which is selectively activated to allow an electric current to flow through it in response to incident light, thus generating an output voltage that is almost proportional to the intensity of the incident light.
The optical spectra, produced through the diffraction of the light beam by the grating 50 into discrete wavelengths, are received by the photodiode array 70, thus being measured in light intensity according to the wavelength. After a measurement of the light intensities of the optical spectra, the photodiode array 70 outputs spectrometric analysis data of the target sample 30 to the signal-processing unit 90. Upon receiving the spectrometric analysis data of the target sample 30 from the photodiode array 70 of the spectrometer head 40, the signal-processing unit 90 reproduces the distribution of light intensities of the spectra, and performs photometric comparisons of the spectrometric analysis data of the target sample 30 with those of a reference sample so as to identify and measure the components and contents of the target sample 30.
FIG. 2 is a flowchart of a spectrophotometry using the conventional spectrophotometer.
As shown in the drawing, the spectrophotometry using the conventional spectrophotometer 100 comprises five steps, that is, a light transmitting step S10, a light diffraction step S20, a light reflection step S30, an intensity measurement step S40 and an intensity distribution reproduction step S50.
At the first step, the so-called light transmitting step S10, a light beam, emitted from the light source 10, is guided to the target sample 30 through the optical fiber 20, and is transmitted through the sample 30.
At the second step, the so-called light diffraction step S20, the light beam transmitted through the sample 30 is received into the reflective diffraction grating 50 of the spectrometer head 40, thus being diffracted to produce optical spectra.
At the third step, the so-called light reflection step S30, the optical spectra of the diffracted light beam are reflected by the concave mirror 60 to the photodiode array 70.
At the fourth step, the so-called intensity measurement step S40, the photodiode array 70 measures the light intensities of the incident optical spectra according to wavelength, thus obtaining spectrometric analysis data, such as the characteristics of the spectra according to wavelength.
At the fifth step, the so-called intensity distribution reproduction step S50, the spectrometric analysis data are transmitted from the photodiode array 70 to the signal-processing unit 90. Upon reception of the spectrometric analysis data from the photodiode array 70, the signal-processing unit 90 reproduces the light intensity distribution and performs spectrometric comparisons of said data with those of a reference sample, thus identifying and measuring the components and contents of the target sample 30. The signal-processing unit 90 is thus able to provide the characteristics of light diffracted into discrete wavelengths.
In the conventional spectrophotometer 100, the photodiodes 80 are linearly arranged along a longitudinal mount at regular intervals xe2x80x9cCxe2x80x9d to form a photodiode array 70. However, the spectrophotometer 100 is problematic in that it is almost impossible to sense light at the intervals xe2x80x9cCxe2x80x9d between the photodiodes 80.
The intervals xe2x80x9cCxe2x80x9d between the photodiodes 80 also reduce the resolving power of the conventional spectrophotometer 100, and so the spectrophotometer 100 is not suitable for use in a precision measurement.
In the prior art, it has been actively studied to linearly arrange an increased number of photodiodes along the mount of a photodiode array to reduce the intervals xe2x80x9cCxe2x80x9d in an effort to solve the problems caused by said intervals xe2x80x9cCxe2x80x9d. However, the linear arrangement of such an increased number of photodiodes undesirably lengthens the signal processing time, and so it is almost impossible to use a spectrophotometer, having a photodiode array with such an increased number of photodiodes, in a real time measurement.
Another problem, experienced with such an increased number of photodiodes of a photodiode array, resides in that said increase undesirably results in a reduction in the size of each photodiode, and so the photodiodes may be easily saturated with light intensity.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a spectrophotometer and spectrophotometry, which uses a precision drive means capable of improving the resolving power during a measurement of light intensity.
Another object of the present invention is to provide a spectrophotometer and spectrophotometry, which uses a precision drive means attached to the photodiode array, thus precisely measuring light intensity while moving as desired.
In order to accomplish the above objects, an embodiment of the present invention provides a spectrophotometer, comprising: a light source used for emitting a light beam having a predetermined wavelength range; a light guiding means for guiding the light beam from the light source to a target sample; a spectrometer head consisting of a light diffracting means for diffracting the light beam transmitted through the target sample to produce optical spectra, a light reflecting means for reflecting the diffracted light from the light diffracting means, a light intensity measuring means for measuring intensity of incident light reflected by the light reflecting means, a drive means for reciprocating the intensity measuring means within a predetermined range, and a stop means for limiting a reciprocating movement of the intensity measuring means; and a signal-processing unit used for reproducing a distribution of light intensities measured by the light intensity measuring means of the spectrometer head.
In the preferred embodiment of this invention, it is preferable to use a multimode optical fiber as the light guiding means.
In addition, it is preferable to use a reflective diffraction grating as the light diffracting means.
It is also preferable to use a concave mirror as the light reflecting means.
In addition, the intensity measuring means preferably comprises a photodiode array, with a plurality of photodiodes linearly arranged on a longitudinal mount at regular physical intervals.
In an embodiment, the drive means preferably comprises a piezoelectric drive unit physically expandable or contractible in accordance with the level of an applied voltage.
In another embodiment, the drive means preferably comprises a bimorph cell consisting of: a piezoelectric drive plate physically expandable or contractible in accordance with the level of an applied voltage; and a piezoelectric fixing plate cemented together with the bimorph piezoelectric drive plate and being physically expandable or contractible in accordance with the level of the applied voltage.
On the other hand, the stop means preferably comprises two stoppers arranged at predetermined positions around opposite ends of the intensity measuring means of the spectrometer head in a moving direction of the intensity measuring means so as to limit the reciprocating movement of the intensity measuring means.
When using a piezoelectric drive unit as the drive means, it is more preferable to use a displacement amplifier attached to the piezoelectric drive unit for amplifying a displacement of the piezoelectric drive unit.
On the other hand, when using a bimorph cell consisting of a piezoelectric drive plate cemented together with a piezoelectric fixing plate as the drive means, the two piezoelectric plates are different from each other in their coefficients of expansion and coefficients of contraction in response to an applied voltage.
Another embodiment of the present invention provides a spectrophotometry using a spectrophotometer with drive means, comprising: a light transmitting step of guiding a light beam from a light source to a target sample through a multimode optical fiber so as to allow the light beam to be partially transmitted through the sample; a light diffraction step of receiving the light beam, transmitted through the sample, into a reflective diffraction grating, thus diffracting the light beam into discrete wavelengths to produce optical spectra; a light reflection step of reflecting the optical spectra of the diffracted light beam by a concave mirror to a photodiode array; a first intensity measurement step of measuring light intensities of the incident optical spectra by the photodiode array; a second intensity measurement step of moving the photodiode array using the drive means by a distance equal to the physical interval between photodiodes of the photodiode array and measuring light intensities of the incident optical spectra at desired positions corresponding to the intervals; and an intensity distribution reproduction step of transmitting spectrometric analysis data, obtained at the first and second intensity measurement steps, from the photodiode array to a signal-processing unit, and reproducing a light intensity distribution of the target sample by the signal-processing unit.